The present invention relates to an ink-jet printer which prints by discharging ink from a nozzle head, having a large number of ink-jet nozzles aligned in the printing direction, toward a printing surface.
In a so-called serial ink-jet printer, nozzle heads for different colors mounted with ink cassettes are reciprocally moved over the entire length in the main scanning direction. During this reciprocal movement, the heads print in units of lines (or in units of 1/N lines) on a printing medium such as plain paper or an OHP sheet. After one line is printed, the printing medium is fed by one line. These operations are repeated to print a predetermined number of lines. For example, Jpn. Pat. Appln. KOKAI Publication No. 10-138520 proposed by the present applicant discloses the following ink-jet printer. This ink-jet printer has a printing speed much faster than the serial ink-jet printer, and it can continuously print on a large number of sheets. This ink-jet printer can be greatly down-sized when compared to an electro-photographic laser printer.
According to the above-proposed printer, a printing medium fed from a paper feeder is sent to a rotary member by a convey mechanism at a predetermined timing and is wound on the circumferential surface (printing surface) of the rotary member. The rotary member is rotated about its center axis in the subscanning direction at, e.g., 120 RPM.
This printer has a nozzle unit provided with nozzle heads for cyan C, yellow Y, magenta M, and black B, which extend in the main scanning direction, i.e., the axial direction of the rotary member, and which align themselves in the subscanning direction, i.e., in the rotating direction of the rotary member. Ink is supplied to the nozzle unit from an ink supply mechanism including an ink tank, a supply pump, and the like. Ink of the respective colors are discharged from the nozzle heads toward the printing medium to print a desired image on the printing medium.
While moving this nozzle unit forward with a reciprocating mechanism for a predetermined distance (e.g., for a distance corresponding to the pitches among the ink-jet nozzles) in the main scanning direction, line printing is performed on the rotating rotary member, i.e., on the printing medium. At the same time, column printing is performed in the subscanning direction by utilizing rotation of the rotary member. Namely, line printing and column printing can proceed simultaneously by utilizing high-speed rotation of the rotary member, so that the printing speed can be greatly increased (by, e.g., 20 RPM). When printing on one page is completed, the nozzle unit is moved backward to the original position, and after that it moves forward to print the next page. After printing, the printing medium is separated from the rotary member and discharged by the discharge mechanism.
In this printer, since the nozzle heads of the respective colors can be disposed at positions remote from the ink tanks of the respective colors, they can be made lightweight to largely increase the reciprocating speed in the line direction. As a result, the printing speed is further increased, and the capacities of the ink tanks of the respective colors can be greatly increased, so 500 sheets or more can be continuously printed.
To continuously print on a large number of printing media as described above, maintenance for clogging prevention and the like is preferably performed for the nozzle heads of the respective colors at, e.g., every three hours. In order to enable this maintenance, the nozzle unit is movable with respect to the rotary member horizontally between a printing position where it can print, and a non-printing position remote from the rotary member by a predetermined distance. After the nozzle head is moved to the non-printing position by a head moving mechanism including a motor, a rack, and the like, maintenance for the respective nozzle heads is performed by using a maintenance mechanism interposed between the nozzle head and the rotary member. When the maintenance is ended, the nozzle unit is moved backward to the printing position by the head moving mechanism, and the gap between the distal ends of the respective nozzle heads and the printing surface is maintained to, e.g., about 1 mm.
When the nozzle unit is at the printing position, it is difficult to establish the gap between the nozzle head and the printing surface quickly and precisely. Since the gap is directly related to the printing quality, the moving mechanism for the nozzle unit must be machined and assembled at high precision. This leads to a complicated structure of the entire printer and an increase in cost.
Even when the nozzle unit can be set at the printing position at high precision, or even when the head moving mechanism is locked after the nozzle unit is set, if vibration or the like of the motor is transmitted from the head moving mechanism to the nozzle unit, or the constituent elements of the head moving mechanism including the motor have backlash, it is difficult to reliably and stably maintain the established gap without fluctuation.
The present invention has been made in view of the above circumstances, and has as its object to provide an ink-jet printer having a simple structure, in which the gap between a nozzle head at a printing position and a printing surface can be established quickly and precisely, and the established gap can be maintained stably.
In order to achieve the above object, according to the present invention, there is provided an ink-jet printer comprising:
a medium holding member for holding a printing medium;
a nozzle unit having a plurality of nozzle heads, each of the nozzle heads having a large number of ink-jet nozzles aligned in a main scanning direction;
an elevating mechanism for vertically moving the nozzle unit between a printing position where the nozzle heads oppose a printing surface of the printing medium held by the medium holding member with a predetermined gap, to print on the printing surface, and a non-printing position above the printing position to be separate from the printing position where maintenance for the nozzle heads is performed;
an engaging mechanism for causing the elevating mechanism and the nozzle unit to engage each other to allow the nozzle unit to be vertically moved by the elevating mechanism when the nozzle unit is between the printing position and the non-printing position, and to disengage from each other so as to set the nozzle unit to be free from the elevating mechanism when the nozzle unit is located at the printing position; and
a head support mechanism for supporting the nozzle unit which has moved to the printing position.
According to the ink-jet printer having the above arrangement, when maintenance for the nozzle heads of the nozzle unit supported at the non-printing position by the elevating mechanism through the engaging mechanism is ended, the nozzle unit is moved downward by the elevating mechanism from the non-printing position to the lower printing position, and is held at the printing position by the head support mechanism. When held at the printing position, the nozzle unit is free from the elevating mechanism. More specifically, the gap between the nozzle heads located at the printing position, and the printing surface is positionally constrained in the vertical direction by only the head support mechanism. Since the printing position is below the non-printing position, the nozzle unit can be stably supported by the head support mechanism by gravity.
After printing is ended, when the elevating mechanism is moved upward, it engages with the nozzle unit through the engaging mechanism with a corresponding time lag. After that, when the nozzle unit moves upward, it separates from the head support mechanism and is moved to the non-printing position by the elevating mechanism.
According to the above arrangement, the gap between the nozzle heads and the printing surface can be established quickly and precisely, and the established gap can be maintained reliably and stably. At the lower printing position, the nozzle unit is separated from the elevating mechanism. As a result, vibration of the elevating mechanism during printing is prevented from being transmitted to the nozzle unit. Therefore, the elevating mechanism need not be strictly vibration-free, so that the structure is simplified and the cost can be reduced.
According to the present invention, there is also provided an ink-jet printer wherein the head support mechanism has a plurality of stationary supports disposed stationarily with respect to an elevating direction of the nozzle unit, and a plurality of movable supports provided on the nozzle unit and supported on the stationary supports at the printing position.
Furthermore, according to the present invention, the head support mechanism includes a three-point support mechanism having two of the stationary supports, which are provided on one side of the printing surface in the main scanning direction, one of the stationary supports, which is provided on the other side of the printing surface, two of the movable supports, which are provided on one end portion of the nozzle unit in the main scanning direction, and one of the movable supports, which is provided on the other end portion of the nozzle unit, the three-point support mechanism supporting the nozzle unit to be movable in the main scanning direction.
According to the above arrangement, the nozzle unit which has moved downward to the printing position can be stably held by the head support mechanism, and the gap between the nozzle heads and the printing surface can be established precisely and stably. When the three-point support mechanism is employed, it can not only hold the nozzle unit in the elevating direction but also the nozzle heads and the printing surface constant three-dimensionally relative to each other, and the positions of the nozzle unit in the main scanning direction can be held in predetermined postures.
According to the present invention, there is also provided an ink-jet printer comprising:
a medium holding member for holding a printing medium;
a nozzle unit having a plurality of nozzle heads aligned in a subscanning direction, each of the nozzle heads having a large number of ink-jet nozzles aligned in a main scanning direction perpendicular to the subscanning direction;
an elevating mechanism for vertically moving the nozzle unit between a printing position where the nozzle heads oppose a printing surface of the printing medium held by the medium holding member with a predetermined gap to print on the printing surface, and a non-printing position above the printing position to be separate from the printing position, where maintenance of the nozzle heads is performed;
a head support mechanism for supporting the nozzle unit, which has moved to the printing position, to be movable in the main scanning direction; and
an elevating guide mechanism which regulates movement of nozzle unit in the main scanning direction and a subscanning direction while the nozzle unit is vertically moved by the elevating mechanism between the non-printing position and the printing position, and which cancels movement regulation in the main scanning direction when the nozzle unit moves to the printing position and is supported by the head support mechanism.
According to the present invention, there is also provided an ink-jet printer comprising:
a medium holding member for holding a printing medium;
a nozzle unit having a plurality of nozzle heads aligned in a subscanning direction, each of the plurality of nozzle heads having a large number of ink-jet nozzles aligned in a main scanning direction perpendicular to the subscanning direction;
an elevating mechanism for vertically moving the nozzle unit between a printing position where the nozzle heads oppose a printing surface of the printing medium held by the medium holding member with a predetermined gap to print on the printing surface with the nozzle heads, and a non-printing position above the printing position to be separate from the printing position, where maintenance of the nozzle heads is performed;
a head support mechanism for supporting the nozzle unit, which has moved to the printing position, to be displaceable in the main scanning direction while regulating displacement of the nozzle unit in the subscanning direction; and
an elevating guide mechanism which regulates movement of the nozzle unit in the main scanning direction and the subscanning direction while the nozzle unit is vertically moved by the elevating mechanism between the non-printing position and the printing position, and which cancels movement regulation of the nozzle unit in the main scanning direction and the subscanning direction when the nozzle unit moves to the printing position and is supported by the head support mechanism.
According to the ink-jet printer having the above arrangement, the nozzle unit is vertically driven by the elevating guide mechanism while regulating its positions in the main scanning direction and in the subscanning direction. When the nozzle unit is located at the printing position, position regulation for the nozzle unit in the main scanning direction by the elevating guide mechanism, or position regulation for the nozzle unit in both the main scanning direction and the subscanning direction is released. In this state, the nozzle unit located at the printing position is supported by the head support mechanism to be movable in the main scanning direction. As a result, vibration from the elevating means in the main scanning direction, or both in the main scanning direction and the subscanning direction is not transmitted. When printing by discharging ink from the nozzle heads to the printing surface, precise printing can be performed without any positional errors in the main scanning direction, or both in the main scanning direction and the subscanning direction.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.